Three-dimensional guide for wire for forming pedicle screw insertion hole and method of producing the same

ABSTRACT

A three-dimensional guide for a wire for forming a pedicle screw insertion hole is produced based on a CT image of a spine, and includes a contact surface section that comes in surface contact with a morphological surface of a bone at an insertion site, and a guide block section that is provided upright from the contact surface section. The guide block section has a guide hole that restricts the insertion direction of the wire. The guide hole has an inner diameter slightly larger than the outer diameter of the wire. The guide hole has a length of 15 to 30 mm to restrict the insertion position and the insertion direction of the wire.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of International Patent ApplicationNo. PCT/JP2011/067955, having an international filing date of Aug. 5,2011, which designated the United States, the entirety of which isincorporated herein by reference. Japanese Patent Application No.2010-181119 filed on Aug. 12, 2010 is also incorporated herein byreference in its entirety.

BACKGROUND

The present invention relates to a three-dimensional guide for a wirefor forming a pedicle screw insertion hole that may suitably be used toinsert a pedicle screw used for spinal surgery into an anatomicallyappropriate site, and a method of producing the same.

Spinal bones allow a motion or movement in an arbitrary direction whilesurrounding and protecting a number of veins, arteries, nerves, and thelike.

An adult human spine is made up of more than twenty distinct bones thatare joined through a posterior intervertebral joint and a cartilageplate (intervertebral disc) that are positioned between adjacentvertebrae.

The spinal bones are anatomically classified into cervical vertebrae,thoracic vertebrae, lumbar vertebrae, and sacral vertebrae.

The cervical vertebrae, the thoracic vertebrae, the lumbar vertebrae,and the sacral vertebrae form a specific curvature referred to as acervical lordosis, a thoracic kyphosis, a lumbar flexure, and a sacralkyphosis.

A pedicle screw may be used during spinal surgery in order to achieve atherapeutic effect by securing the spine.

However, since the configuration of the spine significantly differsamong individuals, and the spine may be deformed to a large extent inpatients who suffer from scoliosis or the like, a severe complicationmay occur when inserting a pedicle screw. For example, quadriplegia dueto spinal injury and death due to vertebral artery injury have beenreported.

A CT cutout technique that develops a life-sized CT image, draws theinsertion position and the insertion angle of a pedicle screw directlyon the CT film, and cuts the CT film along the insertion line and theposterior margin of the lamina has been proposed in The journal of theJapan Spine Research Society 19(1), 2008, p. 31 (author: HiroshiMiyamoto).

The CT cutout technique can accurately obtain the insertion position,but does not reliably ensure the stability of the insertion direction.

SUMMARY

The invention may provide to a three-dimensional guide for a wire thatis used to form an insertion hole for inserting a pedicle screw at ananatomically appropriate position, and a method of producing the same.

According to one aspect of the invention, there is provided athree-dimensional guide for a wire for forming a pedicle screw insertionhole that is produced based on a CT image of a spine, thethree-dimensional guide including a contact surface section that comesin surface contact with a morphological surface of a bone at aninsertion site, and a guide block section that is provided upright fromthe contact surface section, the guide block section having a guide holefor restricting an insertion direction of the wire.

It is necessary to form a pedicle screw insertion hole having ananatomically appropriate depth in the pedicle of vertebral arch in ananatomically appropriate direction when inserting a pedicle screw intothe pedicle of vertebral arch.

In this case, a K-wire is inserted into the pedicle of vertebral arch,and a preliminary hole is formed in the pedicle of vertebral arch alongthe K-wire inserted into the pedicle of vertebral arch using a hollowdrill.

The drill is then removed while allowing the K-wire to remain, and athread is formed in the inner circumference surface of the preliminaryhole along the K-wire using a hollow tap.

One aspect of the invention provides a three-dimensional guide thatcontributes to stabilization of the insertion position and the insertiondirection of the K-wire.

Since the vertebral arch has processes such as a transverse process, aspinous process, and a articular process, it is preferable that thecontact surface section include a morphological surface section thatcorresponds to the morphological surface of the bone at the insertionsite, and a process contact section that comes in contact with theprocess of the vertebral arch so that the position of thethree-dimensional guide is stabilized during surgery. It is preferablethat the guide hole have a length of about 15 to about 30 mm from theviewpoint of insertion stability.

If the length of the guide hole is less than 15 mm, the insertiondirection may become unstable. If the length of the guide hole exceeds30 mm, the height of the guide block increases although the insertiondirection becomes stable.

The three-dimensional guide may be produced by a method that includescapturing a CT image of a spine, extracting a pedicle screw insertionsite based on the CT image, designing the shape of a block that has acontact surface section that corresponds to the morphological surface ofthe bone at the extracted insertion site, producing a mold based on thedesigned shape, and molding the three-dimensional guide in the mold.

Since the three-dimensional guide according to one aspect of theinvention includes the contact surface section that comes in surfacecontact with the morphological surface of a bone, and the guide holethat three-dimensionally guides the insertion direction of the wire, apedicle screw can be safely inserted into an appropriate site (part) ofa spine in a stable manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a bone model of cervical vertebrae, andan example of a three-dimensional guide that is produced to come insurface contact with the morphological surface of the bone.

FIGS. 2A and 2B illustrate an example in which a three-dimensional guideaccording to one embodiment of the invention is brought into contactwith cervical vertebrae to position a guide hole, wherein FIG. 2Aillustrates a state before the three-dimensional guide is brought intocontact with cervical vertebrae, and FIG. 2B illustrates an example inwhich a guide hole 13 is positioned by fitting a process contact section14 to a process 2 of the bone.

FIGS. 3A and 3B are side views illustrating cervical vertebrae, andillustrate an example in which the insertion direction of a K-wire isdetermined using a guide hole 13 so that a vertebral artery 3 is notdamaged, wherein FIG. 3A illustrates a state before thethree-dimensional guide is brought into contact with cervical vertebrae,and FIG. 3B illustrates a state after the three-dimensional guide hasbeen brought into contact with cervical vertebrae.

FIGS. 4A to 4C are cross-sectional views illustrating the positionalrelationship between a pedicle of vertebral arch and a three-dimensionalguide, wherein FIG. 4A illustrates a state before the three-dimensionalguide is brought into contact with the pedicle of vertebral arch, FIG.4B illustrates a state in which a process contact surface 14 a of thethree-dimensional guide that is in the shape of a recess is brought intocontact with a process 2 of the bone, and FIG. 4C is a bottom viewillustrating the three-dimensional guide.

FIGS. 5A and 5B are front views illustrating a state in which athree-dimensional guide is brought into contact with a pedicle ofvertebral arch, wherein FIG. 5A is a partial cross-sectional viewillustrating a state before the three-dimensional guide is brought intocontact with a pedicle of vertebral arch, and FIG. 5B is a partialcross-sectional view illustrating a state after the three-dimensionalguide has been brought into contact with the pedicle of vertebral arch.

FIGS. 6A to 6C illustrate a state in which a K-wire is inserted along aguide hole formed in a three-dimensional guide, wherein FIG. 6Aillustrates a state before the K-wire is inserted, FIG. 6B illustrates astate after the K-wire has been inserted, and FIG. 6C illustrates astate in which the three-dimensional guide is removed from the K-wire.

FIGS. 7A to 7C illustrate an example in which a pedicle is drilled intoa pedicle of vertebral arch along a K-wire using a hollow drill, whereinFIG. 7A illustrates a state in which the K-wire is inserted into ahollow section of a drill, FIG. 7B illustrates a state during drilling,and FIG. 7C illustrates a state after a preliminary hole P₁ has beenformed.

FIGS. 8A to 8C illustrate an example in which the inner circumferencesurface of a preliminary hole is tapped along a K-wire using a hollowtap, wherein FIG. 8A illustrates a state in which the K-wire is insertedinto the tap, FIG. 8B illustrates a state during tapping, and FIG. 8Cillustrates a state after a pedicle screw insertion threaded hole hasbeen formed.

FIGS. 9A to 9C illustrate an example in which a pedicle screw isinserted into an insertion threaded hole formed in a pedicle ofvertebral arch using a dedicated driver, wherein FIG. 9A illustrates astate before the pedicle screw is inserted, FIG. 9B illustrates a stateafter the pedicle screw has been inserted, and FIG. 9C illustrates astate after the driver has been removed.

FIG. 10 illustrates an example in which a plurality of pedicle screwsare connected using a rod.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A three-dimensional guide according to one embodiment of the inventionmay be applied to an arbitrary part of a spine. An example in which thethree-dimensional guide is applied to cervical vertebrae is describedbelow.

The configuration (morphology) of the bones in the operative site iscaptured as a CT image, and a bone model A (see FIG. 1) is formed usingplaster or the like.

Since a spine has a complex configuration in which vertebral arches arejoined through an intervertebral disc, an anatomically appropriateinsertion direction and insertion depth of a pedicle screw aredetermined using the bone model A and the CT image.

A spinal bone (vertebral arch) 1 has processes 2 (e.g., transverseprocess, spinous process, and articular process), and the surface ofeach bone has a complex and irregular configuration.

As illustrated in FIGS. 3A to 4B, a vertebral artery 3 passes throughthe spinal bone 1.

When the insertion site and the insertion direction have beenanatomically determined taking account of the above situation, the shapeof a plurality of (three in FIG. 1) three-dimensional guides 10, 10A,and 10B is determined based on the CT image.

When determining the shape of the three-dimensional guides 10, 10A, and10B, it is necessary to set the size of contact surface sections 11,11A, and 11B that come in surface contact with the bone along theirregular configuration of the bone at the insertion site, and the shapeand the size of guide block sections 12, 12A, and 12B.

The following description focuses on the three-dimensional guide 10, anddescription of the three-dimensional guides 10A and 10B is omitted(corresponding reference signs are used for the three-dimensional guides10A and 10B in the drawings).

The contact surface section 11 may have a process contact section 14that comes in contact with the process (spinous process) 2 of thevertebral arch so that the three-dimensional guide 10 can be positionedby merely bringing the three-dimensional guide 10 into contact with thevertebral arch.

According to this configuration, the three-dimensional guide 10 isnecessarily accurately positioned, and is not shifted due to the shapeof the contact surface section (may be referred to as “morphologicalsurface section”) 11 that is formed by a gradual irregular curvedsurface that corresponds to the morphological surface (morphology) ofthe bone at the insertion site, and the shape of the process contactsection 14 that is formed by a steep slope, by merely placing thethree-dimensional guide 10 in the vicinity of the insertion site.

Since it is necessary to pull out the three-dimensional guide 10 afterinserting a K-wire in order to form an insertion hole for inserting thepedicle screw, the contact surface section 11 and the process contactsection 14 are designed so that an undercut section is not formed.

In one embodiment of the invention, the process contact section 14 has aprocess contact surface 14 a that is in the shape of a recess thatcorresponds to the shape of the spinous process 2 (see FIGS. 4A to 4C,5A, 5B, and 6A). Note that the configuration is not limited thereto aslong as the three-dimensional guide 10 can be effectively positioned.

A guide hole 13 is formed in the guide block section 12 to restrict theinsertion direction of a K-wire 20 while guiding the K-wire 20.

After the shape of the three-dimensional guide 10 has been determined, amold that has the determined shape is produced.

A resin or the like is injected into the mold to produce athree-dimensional guide having a given shape.

The insertion position and the insertion direction of the K-wire can beaccurately determined by placing the three-dimensional guide 10 thusproduced at the insertion site of the spine.

A method of forming a pedicle screw insertion hole using thethree-dimensional guide 10 is described below.

FIGS. 2A and 2B are rear views illustrating cervical vertebrae, andFIGS. 3A and 3B are side views illustrating cervical vertebrae.

FIGS. 4A to 4C are cross-sectional views illustrating a pedicle ofvertebral arch, and FIGS. 5A and 5B are enlarged views illustrating thespinous process 2.

As illustrated in FIGS. 2A, 3A, 4A, and 5A, the three-dimensional guide10 that is produced based on the CT image includes the process contactsection 14 in which the process contact surface 14 a that is in theshape of a recess that corresponds to the shape of the spinous process 2is formed, the contact surface section 11 that comes in contact with themorphological surface of the bone in an area from the spinous process 2to the insertion site of a pedicle screw 50, and the guide block section12 in which the guide hole 13 is formed.

Note that the contact surface section 11 comes in approximately surfacecontact with the morphological surface of the bone. The entire contactsurface section 11 need not necessarily come in contact with the bone.

When the three-dimensional guide 10 is placed on the morphologicalsurface of the bone that corresponds to the operative site, the processcontact surface 14 a that is in the shape of a recess is fitted to thespinous process 2 of the bone, and the contact surface section 11 isfitted to the irregular morphological surface of the bone in an areafrom the spinous process 2 to the guide hole 13, so that thethree-dimensional guide 10 is positioned. Therefore, the insertiondirection of the K-wire 20 is accurately determined by the direction ofthe guide hole 13 (see FIG. 6A).

The K-wire has a diameter of 1 to 2 mm, and the guide hole 13 has aninner diameter slightly larger than the outer diameter of the K-wire. Itis desirable that the guide hole 13 have a length of 15 mm or more.

The stability of the insertion direction is improved as the length ofthe guide hole 13 increases. The length of the guide hole 13 ispreferably 30 mm or less from the viewpoint of insertion operability andproducibility of the guide block section 12.

Since the K-wire 20 is inserted along the guide hole 13 of thethree-dimensional guide 10, the artery 3 and the like are not damaged.

When the K-wire 20 has been inserted into the pedicle of vertebral arch(see FIG. 6B), the three-dimensional guide 10 is removed from the K-wire20 (see FIG. 6C).

A hollow drill 30 is inserted into the pedicle of vertebral arch alongthe K-wire 20 while rotating the drill 30 (see FIGS. 7A and 7B) to forma preliminary hole P₁ (see FIG. 7C).

A tap 40 (tapping drill) is inserted into the pedicle along the K-wire20 and the preliminary hole P₁ while rotating the tap 40 (see FIGS. 8Aand 8B) to form a pedicle screw insertion hole P₂ having a thread groove(see FIG. 8C).

An external thread section 50 a of the pedicle screw 50 is screwed intothe insertion hole P₂ using a dedicated driver 60 (see FIGS. 9A and 9B),and the driver 60 is removed after the external thread section 50 a hasbeen screwed into the insertion hole P₂.

The angle of a head 50 b of the pedicle screw 50 thus inserted isadjusted, and a plurality of pedicle screws 50 are connected using a rod70 (see FIG. 10) to secure the bone 1.

The outer diameter of the external thread section 50 a of the pediclescrew 50 is normally 3.5 to 4 mm.

The three-dimensional guide 10 may be used in many institutions in whichspinal surgery is performed.

Although only some embodiments of the present invention have beendescribed in detail above, those skilled in the art will readilyappreciate that many modifications are possible in the embodimentswithout materially departing from the novel teachings and advantages ofthis invention. Accordingly, all such modifications are intended to beincluded within scope of this invention.

What is claimed is:
 1. A three-dimensional guide for a wire for forminga pedicle screw insertion hole that is produced based on a CT image of aspine, the three-dimensional guide comprising: a contact surface sectionthat comes in surface contact with a morphological surface of a bone atan insertion site; and a guide block section that is provided uprightfrom the contact surface section, the guide block section having a guidehole for the wire, and the guide hole having an inner diameter slightlylarger than an outer diameter of the wire, and having a length of 15 to30 mm to restrict an insertion position and an insertion direction ofthe wire.
 2. The three-dimensional guide as defined in claim 1, thecontact surface section including a morphological surface section thatis formed by a gradual irregular curved surface that corresponds to themorphological surface of the bone at the insertion site, and a processcontact section that is formed by a steep slope and comes in contactwith a process of a vertebral arch.
 3. A method of producing athree-dimensional guide for a wire for forming a pedicle screw insertionhole, the method comprising: extracting a pedicle screw insertion sitebased on a CT image of a spine; producing a mold based on the extractedpedicle screw insertion site; and molding the three-dimensional guide inthe mold, the three-dimensional guide including a contact surfacesection that comes in surface contact with a morphological surface of abone at the insertion site, and a guide block section that has a guidehole for restricting an insertion position and an insertion direction ofthe wire.
 4. The method as defined in claim 3, the molding of thethree-dimensional guide including molding the contact surface section inthe mold so that the contact surface section includes a morphologicalsurface section that is formed by a gradual irregular curved surfacethat corresponds to the morphological surface of the bone at theinsertion site, and a process contact section that is formed by a steepslope and comes in contact with a process of a vertebral arch.